Toxoplasma gondii is an intracellular protozoan parasite that is the causative agent of Toxoplasmosis. Toxoplasma infection in mice provides an excellent experimental model for understanding food borne infections and chronic infections of the brain. The overall goal of this project is to gain a deeper understanding of how the mammalian immune system responds to chronic Toxoplasma infection by tracking parasites and immune cells in the brain. Specifically, we propose to examine how T cell interactions with parasites and invaded host cells changes during progressing versus controlled chronic infection (Aim 1), to investigate the key features that distinguish a protective CD8 T cell response from a non-protective one (Aim 2), and to investigate the role of regulatory T cells in modulating T cell effectors responses (Aim 3).